Tony Stark is a playboy, not only in the Marvel Cinematic Universe but also in Marvel Comics. He would flirt with almost every good looking woman and until he found Pepper Potts, he was never serious about a relationship.
It is really tough for someone like Iron Man to be ever involved in a very serious relationship because he is literally married to the superhero job. He never knows which mission might be his last, so it is better not to commit. Nevertheless, the CEO of Stark Industries has lived long enough in the comic-book world to be involved in a lot of relationships.
10 Sunset Bain
Tony wasn't holding back even during his student life. He was involved in a relationship with an older woman going by the name of Sunset Bain. There was something wrong with her and it was pretty apparent that she was trying to manipulate Tony. Of course, the young man wanted to impress Sunset and he foolishly ended up giving the security code of Stark Industries. Not long after, many prototypes were stolen and Sunset dumped Tony. A lesson learned for the young billionaire.
9 Veronica Benning
There were some dark days that Tony had to get through. He had his back broken once and he hired Veronica Benning as his physiotherapist. During the time when he was trying to re-learn how to walk, he grew close to Veronica. The relationship became intimate but the good days didn't last long. A virus took over Stark and he started abusing alcohol. Not knowing that this wasn't actually Stark, Veronica was disheartened and left him.
8 Emma Frost
The Civil War storyline is considered one of the best of all time due to Iron Man. The comic-book reading fans got to see the evil side of Tony Stark for the very first time. He was recruiting superheroes to his side back then and he met up with Emma Frost.
During his pitch, Stark hinted at the relationship between them, which Emma didn't deny. This was a very unlikely reveal and even though fans never got to see it, they could've guessed that Emma and Stark formed a decent enough pair.
7 Anna Wei
Tony has traveled the world with his armor and one of those times, he found himself trapped in the Republic of Sarawak doing his job of being a hero. His Iron Man suit was broken and one of the locals, Anna Wei offered him a place to stay as a thank-you for saving her son. Over time, they grew close to each other, with Tony having enough time to rebuild his armor. They parted ways when it was time for Stark to leave and they did so on very good terms.
6 Justine Hammer
In a very dark storyline in Ultimate Comics, Tony Stark had to track down his missing technology. Unsurprisingly, it was his grandfather, Howard Stark Sr, who was behind it all. And of course, he hired Justine Hammer to keep a look on Stark. She got close to Iron Man and they began a relationship, only for it to be blown away once Tony learned the truth. Iron Man, inadvertently, ended up killing both Howard and Justine.
5 Natasha Romanoff
Iron Man and Black Widow have been romantically involved several times. The first time things got intimate was when Natasha was still a spy from Russia but as soon as the truth came out, Tony had no choice but to leave her. In Ultimate Comics, though, the writers tried to explore their relationship a bit further and they did look like a very good couple. It was due to them being very good friends. Some would even say that Natasha seemed to like Tony a bit more than Captain America.
4 Bethany Cabe
Bethany Cabe and Tony Stark was a very obvious relationship, once the former joined Stark's security team. Bethany was beautiful, smart, and attractive. Tony was never going to let her pass.
It felt like they were going for the long haul but Tony's drinking problems halted their momentum. And things came to a standstill when Bethany came to know that her husband—who she believed to be dead—is alive. There was simply no coming back from that.
3 Maria Hill
Maria Hill and Tony Stark have worked with each other for quite some time and they have always managed to keep things professional. But during one storyline where it felt like Earth was about to end, they gave in to their desires. They became intimate just for a little while. It took them until morning to become normal again and with bigger things at play, they never got the opportunity to revisit this romantic instance.
2 She-Hulk
She-Hulk has been involved in a lot of casual relationships, with the latest one being the God of Thunder. It isn't a surprise that Jennifer Walters has also been involved romantically with Tony Stark. Their respective personalities are such that they don't really take relationships very seriously and they haven't taken each other seriously either. But it would be wrong to suggest that both She-Hulk and Iron Man never thought about considering each other as a life partner.
1 Wasp
Janet Van Dyne aka The Wasp is one of the most unexpected partners Tony Stark has had. With the Avengers, both Iron Man and Janet have fought together, without the latter knowing the former's real identity. When Janet divorced her husband (Tony's good friend), she got close to Iron Man. Soon, they were involved in an intimate relationship that Captain America didn't like. It was because Tony never told Janet how closely he was related to her ex-husband. As soon as she came to know, everything went downhill.