Vampires can love humans. They just turn them. Also, Michael has no societal pressure against dating whoever he wants.
Why? Just because they are 2 groups which fight?
The only forbidden love in Underworld was between Lucian and Sonja, and it was due more akin to the child of a white slaveowner being in love with a black slave, not members of 2 rival houses.
And again, Michael was never a part of the Lycan clan or the Lycan-Vampire war.