Commitment issues aren't always deal breakers. However, if your partner is unwilling to acknowledge the truth and work on facing the challenge, it will be difficult for the relationship to last over the long term.
The first thing you need to do when dealing with someone who is struggling with engagement is determining whether that relationship is right for you. No matter how much you love and care for someone, a relationship should serve your needs and progress (if you choose to). Ignoring red flags or deal breakers is a surefire way to get into an unhappy relationship.
Ask your partner why they have problems with engagement in the first place, and try to understand their fears about engagement. Don't focus forever, focus on the here and now. In other words, unless you are in the phase of marriage or childbirth, focus on your current situation and moment. Look for improvements. Remember, slow progress is still progress. When you see them try, acknowledge their efforts.
If there is no progress and you don't seem on the same page about the future of the relationship, you may need to end that relationship before one or more parties are seriously injured.