Hello Hatawa, In this context "suck" means being inadequate or undesirable, be extremely bad in quality or just stand still without any change. So he means something like " Life would be meaningless, boring or miserable without you".

My Life Would Suck Without You- lyrics- maybe someone can translate them for you? Guess this means you're sorry You're standing at my door Guess this means you take back All you said before Like how much you wanted Anyone but me Said you'd never come back But here you are again 'Cause we belong together now, yeah Forever united here somehow, yeah You got a piece of me And honestly, My life (my life) would suck (would suck) without you Maybe I was stupid for telling you goodbye Maybe I was wrong for tryin' to pick a fight I know that I've got issues But you're pretty messed up too Either way, I found out I'm nothing without you 'Cause we belong together now, yeah Forever united here somehow, yeah You got a piece of me And honestly, My life (my life) would suck (would suck) without you Being with you Is so disfunctional I really shouldn't miss you But I can’t let you go Oh yeah 'Cause we belong together now, yeah Forever united here somehow, yeah You got a piece of me And honestly, My life (my life) would suck (would suck) without you 'Cause we belong together now, yeah Forever united here somehow, yeah You got a piece of me And honestly, My life (my life) would suck (would suck) without you-

没有你 我的生活实在差劲！