I think I may lose interest in her for physical reasons.
Do you have an obligation to stay with her?
No I don't and I feel like she's not for me.
It's okay that you are not physically attracted to her and have lost interest because of that.  However, you shouldn't leave someone just because they have changed physically. Physical changes will always change again and you may regret having lost her.
Maybe you're right, I'll try to do it.
Relationships are hard. Giving it a try is the only way you'll know for sure.