There are many factors that could have changed since you last were pg. Your hormone levels, he could have a lower sperm count, etc.
How long have you been active in ttc? If under 35, then a year is what they say to give it. If over 35, 6 months. Is seeing your GYN or a fertility doctor (RE) something you would consider? Just even to get baseline testing done, I think can be done through your GYN. Like getting an HSG, his sperm analysis and basic blood work to rule out or in certain problems that could be preventing pg.
can his healthy sperm change in two years? we have conceived once before, but unfortunately I miscarried, but this was two years ago. so I am hoping all his little swimmers are still working properly like they were. I was just having a little doubt because I conceived before, and now i've been trying since feb and still nothing.
i never read that just looking at sperm with the naked eye could tell you anything. The only way I have ever heard or read about was having it checked in lab after a donation was made.
Having your partner's sperm checked is one of the first things that should be done to check for infertility issues.