Knowing the reputation Ibiza has had for many years for sex holidays for single guys my guess is that it's extremely unlikely that that your boyfriend has got an entirely unblemished reputation in that respect.
If he's lied to you over other issues in the past, it's probable that he will do so again in the future at some point. If you don't trust him, dump him now before he has the capacity to hurt you deeply at some point in the future. Trust is all important in any relationship. If it's not there you have absolutely nothing firm to build on.