How to gain self-value?

I have had boyfriends pretty much constantly since I was fifteen (I'm now nineteen and a half). I'm about to break up with my current one (long story) but there's another guy that I'm sort of seeing. Last night I got into an argument with my friend because she was saying it's pathetic to need a boyfriend to feel valued. I agree, but I don't know how else to value myself. Having someone care for me that much as a whole person - value my opinions, want to spend time with me, etc makes me feel I must be worth something, but when I'm alone I can't think of myself as worth anything - I'm only worth what other people think I'm worth. I do have some really good friends, and obviously it matters that they value me, and I would never choose a guy over my best friend, ever, but friends have other commitments and interests - they can go weeks without talking to you as you, i.e. asking how you are, your opinions etc. Whereas a boyfriend spends a lot of one on one quality time with you - plus physical closeness. I don't think this is particularly logical, because there are reasons I should value myself, e.g. I have loving parents, I'm at a top university and have recently been getting firsts, people generally seem to find me interesting and engaging, etc, but I can't help feeling like I just don't have any value. I want to distract myself but I can't because exams are just round the corner and I have to stay in and work all the time - which is mind numbingly dull and I just sit and feel depressed. I was just wondering if anyone can think of any ways to make myself feel valuable regardless of whether i have a boyfriend?