I think you are right in a general sense. By serving people, we are definitely serving God and God did put people in our lives, in part, so that we would glorify him through our interactions with them.

However, I believe that as with all good things, they can also become an obstacle if we don't properly prioritize them. I think it is easy for us to give things the wrong priority and to allow otherwise good things to stop us from doing what we are supposed to be doing. That is what I was referring to. Spending time with my YF is certainly a way to glorify God. But if God has called me to serve in my church and I fail to do it because I would rather be with my YF, then I am disobeying God regardless of the fact I am doing something good. If God called me to go plant a church in some remote region and I refuse to do it because it would mean being away from my YF for several months, then I am not serving God in the way he intended me to despite the fact I can make the excuse that I am serving him by serving my YF; it's not only important to serve God, but also to obey him. Spending time with my YF and showing God's glory through my love for him is a wonderful thing, but it shouldn't be taking up time that God wanted me to set aside for other things. If spending time with my YF is taking precedence over my bible study time, my prayer time, the time I spend serving in other ministries God called me to, etc. there is something wrong despite the fact I can claim to be serving God through my relationship with my YF.