I don't think secondary infertility is unpainful, I really feel for anyone not in control of their fertility, be that women stuggling with ttc dc1,2,3,4,5 or those pregnant when it is unplanned. What I don't think helps the situation is when women feel negative emotions towards other women just because they have what the (ttc) woman wants.
I am at an age where all of my friends have had babies in the last couple of years, it is really hard cooing over a growing bump and talking about birth plans and hearing their fears and happiness but they were not pregnant with my baby and just because i wanted to be pregnant more than anything it didnt make their pregnancy any less special, as a good friend I was there and listened to them and bought them pressies and adored their babies... then went and sat in a hot tub with a large glass of wine and some blue cheese
I understand that everyone is individual but how I choose to cope was by concentrating on the things I do have that are amazing, my OH and my lovely family... and my friends (and new generation of babies!) That is my advice because it worked for me and I didn't even have my own child to concentrate on, I don't expect everyone would agree with my advice but it worked for me!
Now I am pregnant with long awaited dc1 I understand that pregnancy isn't the hollywood inspired fantasy that i thought it was (i am not complaining for a second as i am over the moon to be given the chance to be a mum) I feel lucky and happy but not for a second have i ever felt smug.
I think it makes a difference if your friend knows you are going through IVF, for me most of my friends did know we were having IVF and there was a big problem in what to talk about, they had baby glasses on (like i do now) so eerything was baby related and i was thinming about fertility and sperm samples and injections all the time. They did try to talk about the IVF with me but I found the comments far from helpful "you are so brave having IVF" from my friend who was 8 months pregnant, i didn't feel brave I felt desperate "things weren't this complicated in my day" from my grandpa to which i said "in your day infertile people remained childless" so for me it was easier to talk about carry cots and cloth or disposable nappies than to try to explain infertility/fertility treatments to people. Anyway, sorry for the babble, my point is that I think most people just don't know what to say even if they do know about your treatment.
I really didn't mean to offend.