Not a surprise you are losing feelings, it sounds like there is a disconnect in the relationship.
For that, you need to ask yourself… Do I want to give this an honest shot at fixing it?
If you say yes, then this type of honesty needs to be communicated with him:
Hey, our relationship is in a bad place and I am tired of pretending of being unhappy.
These are the things that I unhappy about, and if we don't fix them, I don't know how we will last.
When a relationship is falling apart, you cannot pretend like everything is okay and allow it to happen. You need to bring attention to it to fix it.
And the other persons reaction will tell you everything you need to know.
If you get a 'I have been feeling the same way, lets develop a game plan to fix this, what other issues are you having?' you're in buisness.
If you get a 'I think we are okay and this is not an issue, I am being defensive and think its offensive that you've suggested this'… the relationship is dead.
Ok how I see it.
His “commitment issues” were because he has always had feelings for her. She wasn’t interested so he started dating you.
He realised he didn’t want to date you because of his feelings for her so you broke up.
Then he realised he still couldn’t have her so he turned to you to soothe his feelings.
He is still emotionally attached to her. You’re second place.
Talking to him won’t work. He won’t understand because he’s wrapped up in her and he’ll probably get defensive.
Not a surprise you are losing feelings, it sounds like there is a disconnect in the relationship.
For that, you need to ask yourself… Do I want to give this an honest shot at fixing it?
If you say yes, then this type of honesty needs to be communicated with him:
Hey, our relationship is in a bad place and I am tired of pretending of being unhappy.
These are the things that I unhappy about, and if we don't fix them, I don't know how we will last.
When a relationship is falling apart, you cannot pretend like everything is okay and allow it to happen. You need to bring attention to it to fix it.
And the other persons reaction will tell you everything you need to know.
If you get a 'I have been feeling the same way, lets develop a game plan to fix this, what other issues are you having?' you're in buisness.
If you get a 'I think we are okay and this is not an issue, I am being defensive and think its offensive that you've suggested this'… the relationship is dead.
I can't believe you're even thinking of staying. Please have some self-esteem.