I think one reason I think its unwise that anyone "give themselves" completely to anyone is my skepticism - my belief we can never know anything (or anyone) completely and absolutely so to "bet all your chips" on one person seems a little hasty and unreasonable. There's a story I could tell about my father that would convey this point but I'm not going to.
We're all just fucked up people looking for a type of absolute solace that will never come. Because part of the human condition is feeling all of these feelings - some of them for good reason, others seemingly for no reason at all. One of the ways we look to feel "whole" is through sex and love. In a way love is just a deeper version of the feeling of validation that sex gives us - because its about someone wanting us rather than just our bodies and for in theory a life time (or for an undisclosed length of time) rather than just one night. But we shouldn't put our emotional baggage on other people. That's why I don't think its wise to ever get too close to anyone. I'm not saying people should never have emotional connections to anyone - far from it - and of course people should do what feels right for them, there's no "correct way" when it comes to how to feel and how to live; but ultimately I feel that not becoming psychologically and emotionally dependent on another human being is always a good thing. Basically what the Epicureans, Stoics and Buddhists advise among others.
I feel like if people expressed how they really felt, and were more genuine, the world would be a better place. But there's a difference between expressing yourself to someone else and clinging to someone else because you've shown them your vulnerabilities. There's nothing wrong with being vulnerable, it's necessary to some degree for any type of closeness or connection, but again, there's a difference between being vulnerable and being psychologically dependent. I think complete psychological independence is an impossibility though; human beings naturally react and are determined by their relations with others - like societal relations interdependence is probably the best course.