To start, I want to point out that I was never in a real relationship with this person.  We started out as a friends with benefits, my first and last, and started to hang out a lot.  We ended up talking everyday, hooking up, and going on dates for about a year.  I mentioned wanting to be exclusive several times, but he told me he didn't think he could handle a relationship with his mental health the way it is.  I knew he was hooking up with other people, but I accepted this was as far as we would ever get.

In December of last year, a girl was added to a groupchat made by our mutual friend.  She messaged me separately when she discovered that he and I knew each other, telling me that they've been talking for two weeks.  I asked him about it, before I realized she meant romantically, and he told me they met on tinder.  At this point, she started asking me about him as a person, telling me how she really liked him and that he seemed like a really great guy.  I didn't know what to tell her, because I didn't want to be the mean girl who gets all jealous even when I have no right to be, so I tried to say relatively positive things about him.  It was incredibly painful, and afterwards I told him I couldn't handle continuing our relationship the way it was.  Knowing he was seeing other people was one thing, but to actually meet her was all too real.

He cut off his relationship with the girl, which I was only certian of when she texted me after asking if he and I were in a relationship, but still said he couldn't handle more.  He just kept telling me that I was the most important person in his life.  It was so painful to hear, but I told him we could only be friends at this point.  Later that week, we met in person.  He told me that he couldn't handle being friends because he loved me, so he wanted us to stop talking for a while.  He then told me that he hoped to get his mental health in order over the next semester, and then hopefully we could begin again in the Summer.  We've spoken a few times since then, mostly resulting from drunk texts, and I can't seem to get over him.

About a month after we stopped seeing each other, a started dating someone else.  I know it looks like a rebound, but we've been dating for 4 months, and I care about him deeply.  I did not intend to jump into a new relationship, but I am happy with him.  I am, however, not sure if I'm over my ex, and I really don't want to hurt the guy I'm with.  He's incredibly sweet and giving, and I love spending time with him, but I wonder if the timing is just too difficult.  I just feel stupid giving up something that is so good because of lingering feelings for someone who I have no future with.  

I would really love some advice as to what would be fair to my boyfriend.  Should I keep trying to put my ex out of my head while in this relationship?  Or should I end things to focus more deeply on moving forward?  Or should I ask to take a break?  In theory, that feels like the best option, but I feel like when people take a break it might as well be a breakup.