If you find that you're constantly questioning whether you measure up to your partner's expectations, your relationship might be one-sided.
If you end up apologizing for every single fight, it’s time to think deeply about your relationship.
The more frequently you justify your partner's behavior to friends, family, and work, the more likely it is that they are seeing something else that you don't.
If you feel so unsettled that you can't stop analyzing how you can be more alluring, and what you can say or wear to keep your partner interested, that could be a sign.
A one-sided relationship occurs when everything else is more important than you.
Is it you who makes all the plans, does all the chores? If so, consider stopping.