I think that when you learn to be protective of yourself and need to stay that way you begin to lose the ability to feel things for other and things that should generate some emotional response.
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Humans are very much hardwired for intimacy and sexual relationships. Taking the path of choosing not to love someone because you want to protect yourself ultimately doesn't protect yourself. It can lead to depression. There's a correlation between sex and longevity. There's a correlation between a good marriage and longevity, when you factor out domestic violence. Given how healthy sex is, I believe it's not mere correlation, it's causation.
If you feel like you have nothing to offer in terms of a relationship, then you should try to make yourself into a person who has much to offer. Even if you never find a relationship, becoming a person who has much to offer has many other benefits. People who don't make themselves into someone with a lot to offer tend to become sullen and withdrawn in many other aspects which can affect friendships and career.
So it will be very profitable in many ways to turn yourself into someone who has a lot to offer. Then, you can start looking for that person who you can love and who will love you in return. Perhaps some good therapy might be very beneficial to you.