I don't think it is at all unreasonable to be angry. My oldest friend killed himself completely unexpectedly 18 months ago, he left a wife and young children, and many hertbroken friends, as well as his parents both still being alive. I was very angry, most of all I could not see how he could do that to his mother. It seemed pretty unforgiveable.
This was a man who was a very senior professional, was also successful in a creative hobby (not wanting to give too much info), had what appeared to everyone to be a highly successful life, materially very well-off (both in his own right and from a very well-off family), lots of friends, lovely and intelligent wife, gorgeous children, and the whole thing was such a shock and seemed incomprehensible. And selfish. And just deeply deeply unecessary and stupid.
After the initial shock (which lasted for months) the anger mellowed, and I was able to think about his situation in terms of the mental health problems which he undoubtedly must have had (unknown to any of his friends). I work in the field of mental health, and with anyone else, patients etc, I would have (and indeed I have, with patient suicides) thought about it like that from the outset, but when it is so personal it is hard to see clearly though the emotions. Over time your feelings will change. Don't beat yourself up about feeling angry, it is completely understandable at this stage. And it's not like you have a choice, if that is how you feel.
What can control is who you express the anger to, of course. With my friend's suicide, a lot of his friends all communicated to each other that we felt angry, but no-one (as far as I know) said that to his wife or his parents.