I think this is a very strange argument. I think though, we need to examine entropy. Entropy is a concept associated with thermodynamics, in terms of how much useful work can be gained from energy. In its generalised form, the laws of thermodynamics say entropy is far more likely to increase over time in a mechanical system.
Clearly, sex and procreation involve the expenditure of energy and the creation of entropy. It doesn’t matter whether the couple in question are having heterosexual sex or homosexual sex. In the case of the heterosexual couple, where conception occurs, the embryo (and later the foetus) requires a lot of energy (name removed by moderator)ut from its environment to survive. The laws of thermodynamics may allow for the entropy to be reduced locally (a foetus is a more organised system than a brick for example) but overall, the life of the foetus will still contribute to the entropy of the universe, as will the sex of its parents and the sexual activities of the homosexual couple. Even if no homosexual sex ever occured, that would make little difference to the overall entropy of the universe. That is determined by much greater factors operating on timescales much longer than a fleeting human lifetime.
Personally, I don’t think a moral conclusion can be drawn trying to relate homosexuality, entropy, and suicide. The first issue is about a sexual orientation and certain sex acts. The second is a complex theory of physics which in itself, is amoral and has no clear relevance to moral issues. The third is that suicide is a deliberate act of ending one’s own life. I don’t see how the three are connected, or how a connection can be made. Even if ‘sin’ is invoked, ‘sin’ is a theological concept and also to a certain extent, a moral concept. But I don’t see how ‘sin’ can have any effect on the laws of physics, or how a concept drawn from physics and expressed in mathematical terms, has any relevance to ‘sin.’ I am inclined to think this is an example of the fallacy of trying to derive an ‘ought’ (moral obligation) from what is (blind natural laws).