When you have doubts about a relationship, how can you tell when you're just splitting or when you really need to move on to someone else?

For so many relationships I've sacrificed much of what I want for the sake of the other person, I think in hope of them thinking I was everything they want and wouldn't leave me. I'm trying to put me first in a healthy way, so I dont have explosive emotions and behaviors from people pleasing all the time.

I've been with my SO for about a year and a half. He has grown increasingly less affectionate and that is something I need a lot of in a relationship in order to feel secure and loved. I also want him to be aggressive with me sometimes and his personality is not like that at all. Part of me feels guilty for having the feelings I have, and I feel like I should not want affection to feel loved nor should I want someone to be physically aggressive with me (like grabbing my body or to kiss me, or pushing me up against a wall, etc). But I do want these things and he hasn't really been able to provide them consistently. I also love him and think I should accept him as he is, but I'm not happy. He also is not very athletic, which I am and want someone to be active with. Otherwise, he's pretty wonderful and patient and kind....and I love him more than I can put into words. I just have this itch feeling that it's not what I need in a relationship. He is also very very emotional and sensitive and I dont think having two people as sensitive as us is helpful for either person.  It breaks my heart to know how much leaving him is going to hurt him. But maybe not more than I'm already hurting him by staying in the relationship when I'm not happy? I've been thinking about cheating and I hate myself for it. Just to see if I'm really wanting this or if it's just one of those I see someone else for a week and I realize it's not what I actually want. It also makes this difficult that he just moved into my apartment a month ago after his lease ended, unexpectedly, a month early. So he also has nowhere to go except his mother's house, and there are a lot of issues there.

Emotions are so complex and challenging to figure out.