Can adopting a cat make your dog feel ignored? We want to get a cat and currently have a small 4 year old dog. He is our only pet and a havanese with a bit of small dog syndrome and we want to get a Siberian cat but won't if it'd make him feel bad

Yes

I don't think a dog knows what 'ignored' even means .. But, some animals do possess jealousy and rivalry.  However, that does not mean ALL animals feel that way when a new member of the family (or as in the animal kingdom, pack) comes along.  There may be a bit of an adjustment period, but .. If you handle it right, both pets may get along just fine.

Well, quite possibly.

But when a young child winds up with a new brother or sister, he usually adapts.

So can your dog, with a little help and attention from you.