That which we imagine, desire and expect without reservation usually occurs.
In relationships, however, it very often happens that one person expects the other to be in a certain way, or to do certain things. Consciously or otherwise, they expect this in order for the other to make them happy. Such an apparently desirable and selfless utterance as "I love you" can often be understood to carry the meaning "therefore I am giving you the responsibility of being and doing what keeps me happy."
This can cause disappointments and suppressed or repressed anger.
The other person has their own desires, and imagines and expects these to occur to suit them. This may produce a quite different result from that expected by the first person. It mostly does!
That is why we communicate.
We communicate to find the differences in others that make life richer and more interesting. We communicate to share our unique differences respecting and cherishing them as they are. We communicate to find out whether we are wanting sufficiently similar realities to include each other in a shared life.
You can expect that 'someone' be part of a future that you imagine, desire and expect, but you may be disappointed if you choose a person and then expect that particular person to be and do what you imagine and want them to be and do.
To desire someone to come into your life and then get to know and accept them as they are is much more exciting.
So if you find that some person in your life is not meeting your expectations maybe it is the expectations that need to be changed.
When you say "I love you" love that person just as they are. Just as they are being, doing and having.