The only way is to have a very honest conversation with your partner. Only you two know if your feelings are strong enough to continue the relationship.

Communication is the key here. It may be the hardest conversation you'll have but honestly, it will be worth it. You don't want to be stuck in a dead-end relationship that's going nowhere, and at the same time, you don't want to throw away a good thing if there's nothing wrong with it. Talk to him/her and ask tactful yet direct questions about how he feels how things are going.