Hi. Welcome. I am a Licensed Master Social Worker with more than 20 years experience working with individuals and families on a variety of issues.
Of course the adjustment is hard...the feelings you are having are very valid. You have lost your husband and have opened your heart....this man moved in for whatever the circumstances were, and now he has left and that can bring up tremendous feelings of loss for you all over again. It is not being needy it is about your desire to spend time with him and it is also about your feelings of loss. Both or valid.
So, I would try and have a conversation with him when you are both feeling calm and maybe explain it from that perspective. you enjoyed living with him and now that has changed...that would be hard for anyone who has feelings for the other person.
I am here when you come back online and will be available until 10pm Easter Standard Time. I will also be back working in the morning. I know it is late for you in the uk. I look forward to talking with you when you are available.