“I don't trust people who don't love themselves and tell me, 'I love you.' ... There is an African saying which is: Be careful when a naked person offers you a shirt.” - Maya Angelou
When we enter into a romantic relationship with a person is unhealthy or simply does not believe him or herself worthy of love, the end result is often that we become responsible for their emotional well-being. We as the ostensibly stronger partner become a source of strength and a "need" for the person.
In an intimate relationship, this is an inherently imbalanced and unhealthy dynamic insofar as it is a crutch that allows a person to continue walking around without a shirt on, to extend the metaphor. Any "love" this person offers is not sourced from a place of genuine happiness, so to some extent it simply cannot be trusted. When a person who does not love himself says "I love you", it can be translated to something more akin to "I love that you make me feel better about myself" or "I need you in order to feel whole" or "thank you for loving me, because I do not know how to love myself."
In my work and personal life, I observe other people doing this all the time. Some of us are just attracted to "projects". You know, those broken souls that really need us to help them. This is highly attractive to those of us who are emotional givers and healers, because in helping them, we find a sense of value and satisfaction. (It also allows us, conveniently, the option to focus on their issues and avoid dealing with our own.)
Sometimes we don't even know that that is happening until we are full-on in a Relationship (or to a lesser degree this can happen in a friendship as well. It just tends to be more evident when a friendship is imbalanced). We may feel like we are the best thing for this person. The notions "I'm the only one who really understands her" or "but he needs me" can be extremely compelling.
What we really do in these scenarios, however, is do ourselves and our partner a disservice. We are selling ourselves short by investing in someone who simply hasn't the capacity to love us back fully because he hasn't learned to love himself yet. And we are enabling the person we care about to use our love as a crutch to prop her up and provide her with a sense of worth.
The hard lesson is: it is not my job to make you feel better about yourself. Neither is it yours for me. The only way we can have a healthy relationship is if we meet at the intersection halfway between our own respective self-loves and self-awareness. The only true intimacy will be found when we are both whole and both bringing our full, best, authentic selves. Or, another way to put it: when we both have our own shirts on.
Only a person who knows, loves, and accepts himself fully and authentically can feel comfortable in vulnerability and intimacy. A person who wants you in his life because you are good to each other and make one another's lives more satisfying is a person worth investing in. However, if you feel "needed", there is a strong probability that there is some unhealthy or codependent stuff going on in the relationship.
Need is a burden, whereas want or desire is a gift. Sometimes it is difficult to tell the difference, but that's part of the work we need to do in order to position ourselves to have the kind of relationships we deserve.
TL; DR: Find somebody who has their shit together and their shirt on.